Physiology Flashcards
Where does excitation in the heart originate?
In pacemaker cells in the SA node
Where is the SA node located?
In the upper right atrium close to where the superior vena cava enters
What is the normal rhythm of the heart called?
Sinus rhythm
What do the pacemaker cells in the SA node generate?
Spontaneous pacemaker potentials
When is an action potential generated?
When the spontaneous pacemaker potential takes the membrane potential to a threshold, an action potential is generated
What is the pacemaker potential?
The slow depolarisation of membrane potential to a threshold
What is the pacemaker potential due to?
A decrease in K+ efflux
Na+ and K+ influx (funny current)
Transient Ca2+ influx (T-type Ca2+ channels)
What happens when threshold is reached?
An action potential is generated
What causes the rising phase of an action potential in pacemaker cells?
Depolarisation. Caused by activation of long lasting (L-type) Ca2+ channels, resulting in Ca2+ influx
What causes the falling phase of action an potential in pacemaker cells?
Depolarisation. Caused by inactivation of L-type Ca2+ channels and activation of K+ channels resulting in K+ efflux
What junctions allow cell to cell spread of excitation?
Gap junctions
Where is the AV node located?
At the base of the right atrium
What property of the AV node allows for heart contraction coordination?
It has a low conduction velocity allowing there to be delay between atrial and ventricular contraction
What is the Bundle of His?
A bundle of nerves fibres which carries the impulse from the AV node to the ventricles where the impulse passes upwards via Purkinje fibres in the ventricles
What is the resting membrane potential of atrial and ventricular myocytes?
-90mV
